Single File Components concept in Vue

Introduction

Single File Components let you keep your HTML, JavaScript, and CSS for a Vue component all in one file. This makes your code neat and easy to manage.

When building a Vue app and you want to organize each component's code in one place.

When you want to reuse a component with its own style and behavior easily.

When working in a team so everyone can understand and update components quickly.

When you want to separate your app into small, manageable pieces.

When you want to use Vue's tooling that supports these files for better development experience.

Syntax

Vue

<template>
  <!-- HTML goes here -->
</template>

<script setup>
// JavaScript goes here
</script>

<style scoped>
/* CSS goes here */
</style>

The <template> block holds the HTML structure.

The <script setup> block contains the JavaScript logic using Vue's Composition API.

Examples

A simple button component that counts clicks. The style applies only to this component.

Vue

<template>
  <button @click="count++">Clicked {{ count }} times</button>
</template>

<script setup>
import { ref } from 'vue'
const count = ref(0)
</script>

<style scoped>
button {
  font-size: 1.2rem;
  padding: 0.5rem 1rem;
}
</style>

A heading component showing a title with scoped styling.

Vue

<template>
  <h1>{{ title }}</h1>
</template>

<script setup>
const title = 'Hello Vue Single File Component'
</script>

<style scoped>
h1 {
  color: teal;
}
</style>

Sample Program

This component lets the user type their name. It updates the greeting below as they type. The input has an accessible label, and styles apply only inside this component.

Vue

<template>
  <div>
    <input v-model="name" placeholder="Enter your name" aria-label="Name input" />
    <p>Hello, {{ name || 'stranger' }}!</p>
  </div>
</template>

<script setup>
import { ref } from 'vue'
const name = ref('')
</script>

<style scoped>
div {
  max-width: 300px;
  margin: 1rem auto;
  font-family: Arial, sans-serif;
}
input {
  width: 100%;
  padding: 0.5rem;
  font-size: 1rem;
  border: 1px solid #ccc;
  border-radius: 4px;
}
p {
  margin-top: 0.5rem;
  font-size: 1.2rem;
  color: #333;
}
</style>

Important Notes

Use scoped on the style tag to keep CSS inside the component only.

The <script setup> syntax is simpler and recommended for Vue 3.2+.

Single File Components work best with build tools like Vite or Vue CLI.

Summary

Single File Components keep HTML, JS, and CSS together for easier coding.

They help organize your app into small, reusable parts.

Scoped styles prevent your CSS from affecting other parts of the app.

Practice

1. What is the main purpose of a Vue Single File Component (SFC)?

easy

A. To write only JavaScript code without any HTML or CSS

B. To separate HTML, CSS, and JavaScript into different files

C. To keep template, script, and style in one file for better organization

D. To create components without any styling or templates

Solution

1. Step 1: Understand the structure of a Vue SFC

   A Vue Single File Component combines template (HTML), script (JavaScript), and style (CSS) in one file for easier management.

2. Step 2: Compare options with this concept

   To keep template, script, and style in one file for better organization correctly describes this purpose. Options B, C, and D contradict the idea of combining all parts in one file.

3. Final Answer:

   To keep template, script, and style in one file for better organization -> Option C

4. Quick Check:

   Single File Component = Combined template, script, style [OK]

Hint: SFC means all parts in one file for neatness [OK]

Common Mistakes:

• Thinking SFC separates files instead of combining
• Believing SFC is only JavaScript code
• Ignoring the style section in SFC

2. Which of the following is the correct way to define the style section in a Vue Single File Component to apply styles only to this component?

easy

A.

B.

C.

D.

Solution

1. Step 1: Recall how scoped styles work in Vue SFC

   Using the uses the correct 'scoped' attribute. Others like 'global', 'module', or 'isolated' are incorrect or unrelated here.

2. Final Answer:

   <style scoped> ... </style> -> Option A

3. Quick Check:

   Scoped style = <style scoped> [OK]

Hint: Use 'scoped' attribute to limit styles to component [OK]

Common Mistakes:

• Using <style> without scoped causes global styles
• Confusing 'module' with 'scoped' attribute
• Trying non-existent attributes like 'isolated'

3. Given this Vue SFC snippet, what will be displayed when the component renders?

<template>
  <div>{{ message }}</div>
</template>

<script setup>
const message = 'Hello Vue!'
</script>

medium

A. undefined

B. Hello Vue!

C. {{ message }}

D. Error: message is not defined

Solution

1. Step 1: Understand template interpolation

   The template uses {{ message }} which displays the value of the 'message' variable from the script.

2. Step 2: Check the script setup variable

   The script setup defines 'message' as 'Hello Vue!'. This value will replace {{ message }} in the template.

3. Final Answer:

   Hello Vue! -> Option B

4. Quick Check:

   Template interpolation shows variable value [OK]

Hint: Variables in script setup show in template with {{ }} [OK]

Common Mistakes:

• Thinking {{ message }} prints literally
• Assuming message is undefined without export
• Confusing script setup with normal script

4. Identify the error in this Vue Single File Component:

<template>
  <button @click='increment'>Count: {{ count }}</button>
</template>

<script setup>
let count = 0
function increment() {
  count++
}
</script>

medium

A. The script setup block cannot contain functions

B. The increment function is missing parentheses in the template

C. The template syntax for event binding is incorrect

D. The count variable should be a ref to be reactive

Solution

1. Step 1: Check reactivity of count variable

   In Vue 3 script setup, to make a variable reactive and update the template, it must be a ref or reactive object.

2. Step 2: Analyze the code

   Here, count is a plain number, so incrementing it won't update the template. It should be defined as const count = ref(0).

3. Final Answer:

   The count variable should be a ref to be reactive -> Option D

4. Quick Check:

   Reactive state needs ref() or reactive() [OK]

Hint: Use ref() for reactive variables in script setup [OK]

Common Mistakes:

• Forgetting to import ref from 'vue'
• Thinking functions can't be in script setup
• Misusing event binding syntax

5. You want to create a reusable Vue Single File Component that accepts a title prop and displays it inside an <h1> tag. Which of the following is the correct way to define the prop and use it in the template?

hard

A.
{{ title }}

B.
{{ props.title }}

C.
{{ title }}

D.
{{ title }}

Solution

1. Step 1: Understand how to define props in script setup

   In Vue 3 script setup, props are defined using defineProps(), which returns an object with prop values.

2. Step 2: Check how to use props in template

   Since defineProps returns an object named props, you can destructure or use the props object. But Vue automatically exposes props keys as variables, so {{ title }} works if you assign props to a variable.

3. Step 3: Analyze options

   {{ title }}

   correctly defines props and uses {{ title }} in template.

   {{ props.title }}

   incorrectly uses {{ props.title }} in template (props is not exposed automatically).

   {{ title }}

   wrongly assigns defineProps to title.

   {{ title }}

   does not use defineProps.

4. Final Answer:

   Option A correctly defines and uses the title prop -> Option A

5. Quick Check:

   Use defineProps() and {{ title }} for props [OK]

Hint: Use defineProps() and {{ title }} to access props [OK]

Common Mistakes:

• Using props.title in template without destructuring
• Assigning defineProps() result to wrong variable
• Not using defineProps() at all